In known systems, the supply of current to a microprocessor which controls various functions in an automobile may never be totally interrupted, since the microprocessor controls functions as, for example, the alarm system of the vehicle or electrical door-locking devices. Since microprocessors draw much more curent than CMOS building blocks and may draw, for example, 50 to 60 mA, use of a microprocessor would cause the battery to be discharged within a few days if the vehicle is not driven and therefore no recharging occurs.